The fast pyrolytic production of liquids from biomass has progressed with the development of improved techniques. Such liquids are termed BioOil. BioOil is a generic term known in the industry and is produced by converting organic residues such as forest and agricultural wastes in a fast pyrolysis process. BioOil is thermally unstable, being prone to polymerization/carmelization and thermal cracking when exposed to elevated temperatures for prolonged periods of time. These products are in the form of gasses, aerosols, vapours and char. In this process, the char is first removed with cyclone separators. Because of the thermally unstable nature of the BioOil product normal surface condensers are inefficient and subject to extreme fouling. As well, the BioOil vapour is subject to chemical degradation. Consequently most processes follow the cyclone separators with a quench tower for rapid cooling, condensation and coalescence of the BioOil. Nevertheless, there remains a significant amount of stable aerosols in the effluent gas stream. Filtration or electrostatic precipitations are usually employed to clean the gas stream further. These systems are not ideal as they suffer variously from high-pressure drops, expensive maintenance or high capital cost. Thus is especially so for biomass feedstocks rich in resins and waxes, such as sugar cane bagasse and bark rich wood residues.
There are different types of the equipment available in industries such as oil and gas processing plants, which collect aerosol and liquid droplets from a gas stream such as scrubbers, filters, wet cyclones, mesh pad and impingement type separators. However, these are ineffective in capturing BioOil droplets and sub-micron aerosols.
BioOil droplets, which appear as liquid droplets, and sub-micron aerosols have different properties from hydrocarbon aerosols. Whereas hydrocarbon liquid evaporates at moderates temperatures, BioOil droplets are very sticky and will polymerize and eventually form coke if heated. Because of the sub-micron size of the aerosol, it is not possible to collect the entire aerosol with the above-mentioned equipment without special filters. The concentration of aerosol and liquid droplets constitutes approximately 20% of the BioOil production. Because of BioOil stickiness and the presence of other particles, filters will foul quickly.
Such filters are very expensive to replace and have problems associated with waste disposal.
The thermolysis/pyrolysis process and BioOil production with feedstocks that contain some wax and different types of extractives cause serious problems in the BioOil production process. These problems lead to an increase in production and maintenance costs. Problems such as equipment fouling, coking/caramelization and polymerization of BioOil aerosols in the gas compressor, gas heat exchangers and electrostatic precipitator increases the production and maintenance cost and makes the continuous operation of the process difficult and expensive.
Techniques for separating aerosol and waxy components from the non-condensable or recyclable gases produced in a pyrolysis/thermolysis of biomass process, especially when using bark and bagasse which contain wax and extractive, were previously unknown. Devices such as cyclones, scrubbers, filters, mesh pads and impingement type separators are not able to collect sub micron BioOil/wax aerosol from the gas stream at a low operation and maintenance cost.